I04 



KNOWLEDGE & SCIENTIFIC NEWS. 



[May, 1904. 



Conducted hy F. Shili.ington Scales, f.r.m. 



MITES. 



Cecil \\'ARBrRTOx, M.A. 

 Why do so few people collect mites ? If we come to think 

 of it the waste of energy among collectors is appalling, 

 simply because nearly all are content to follow beaten 

 tracks, where the chances of new discoveries are rare, 

 and the same old observation is made for the fifty- 

 thousandth time. There must be hundreds of people in 

 England at this moment whose hobby is the microscope, 

 who are skilful in the manipulation of small objects, and 

 possess the collector's instinct, but whose imagination 

 does not get beyond making neat preparations of dia- 

 toms or rotifers, or Foraminifera. And all the time here 

 is a group of creatures ideal for the purpose, of great 

 intrinsic interest, and concerning which a great deal 

 remains to be discovered. Anyone who attacks the 

 Acari with enthusiasm is pretty sure to add not one but 

 many mites to the sum of human knowledge. 



Many, no doubt, are deterred by the very fact that so 

 little is known about these creatures. A moth, or a 

 beetle, or a rotifer can generally be identified wath com- 

 parative ease, because the researches of innumerable 

 workers in these groups have been reduced to a form 

 convenient for reference ; but how is one to identify a 

 mite ? There is force in this argument, of course, though 

 if the difficulties are greater, the chances of distinction 

 are greater in proportion. In one family of the Acari, 

 the Oribatida- or " beetle-mites," moreover, this difficulty 

 does not exist. Just consider, for a moment, the follow- 

 ing facts. 



Hardly a single Oribatid mite was recorded as having 

 been captured in this country before 1879. In that year 

 Mr. A. D. Michael published the first of a series of 

 papers on these creatures, which he has since summed 

 up in an admirable monograph,'' fully illustrated, and 

 containing every kind of information which can be of 

 use to the collector. In this about a hundred British 

 species are described. Remember that he was absolutely 

 a pioneer in the subject, and worked at it almost single- 

 handed in the leisure hours of five years of a busy pro- 

 fessional life, and that very little indeed has been done 

 since. He has given his followers a magnificent start : 

 but is it likely that the mine he discovered and worked 

 so enthusiastically is anywhere near exhaustion ? 



It would appear at first sight that the search for 

 creatures which seldom e.xceed a millimetre in length, 

 and are frequently very much less, must be laborious 

 and irksome. The exact opposite is the case. Cer- 

 tainly it would be out of the question to go out into the 

 open, armed with a lens, in search of individual mites, but 

 there is not the least need for such a proceeding. These 

 mites live under loose bark, in decaying wood, and 

 especially in lichen and moss. The necessary equip- 

 ment, then, for field work is not a lens at all, but a bag, 

 or several bags. Thus armed the collector starts out to 

 visit some likely spot that has occurred to him, a moss- 

 grown wall, or a coppice where the trees are grey with 



• Publications of the Royal Society, 2 vols. 



lichen, and the ground carpeted here and there with 

 patches of moss, and with such materials he fills his 

 bags, bringing them home to work over at leisure. 



The study or "den" is now cleared for action. The 

 apparatus consists of a pocket-lens, some large sheets of 

 white paper (the white under-surface of remnants of 

 wall paper is excellent for the purpose), a camel's hair 

 brush, some ordinary microscope slides, and a low-power 

 microscope arranged for opaque objects. I know of 

 nothing better for the work in hand than a Stephenson's 

 binocular with the one-inch objective. Portions of the 

 moss are shaken out over the paper, and the dihris 

 allowed to remain undisturbed for a minute or so. Then 

 most of the creatures shaken out of the moss will have 

 found their feet, and will not be dislodged if the general 

 litter is gently tilted off or blown aside. Numerous little 

 specks are sure to be left adhering to the paper, and a 

 moment's observation will show that some of them are 

 slowly moving. Then the lens is brought into play, 

 and the moving speck examined, and if it seems to be 

 one of the creatures sought, it is transferred to a slide by 

 means of the brush, and placed under the microscope for 

 a closer study. But there are many other moving 

 specks, and time is too precious just now to spend more 

 than a moment or two o\er a single example, so w'e 

 lightly place a cover-slip on his back, and thus loaded he 

 is not likely to have moved \ery far when we ha\'e 

 leisure to look at him again. 



If the material is good, the hunt will be found exciting 

 enough while it lasts, and the '• bag " will be a certain 

 number of tiny creatures making ineffectual efforts to 

 walk along on the slippery surface of the glass slides 

 under the superincumbent weight of the cover-slips. 

 What is to be done with them ? Well, the more 

 thoroughly they can be examined while alive, the better, 

 but those that are selected for the cabinet have to be 

 killed and preserved in some way or other. In a 

 collection of mites it is very desirable to have a double 

 series of specimens, one series mounted as opaque 

 objects, and the other rendered transparent. Whichever 

 their destination, the preliminary operations are the same. 

 The best w'ay to kill them is to pop them into boiling- 

 water. It sounds brutal, but it is instantaneous, and it 

 has the advantage that it causes many species to extend 

 their legs, and those that are not so obliging are generally 

 in a more or less limp condition, and pretty easily mani- 

 pulated. Now is the moment when the skill of the 

 operator comes in. The mites are taken out of the 

 water with the brush, and placed on white blotting 

 paper. Then a single specimen is placed on a slide, 

 turned on his back, and his legs arranged in the desired 

 attitude under a dissecting microscope. A cover-slip 

 keeps him in the proper position, and a drop of 2";', 

 solution of formalin is run in, a slight weight, such as a 

 flattened shot, being superimposed to prevent the legs 

 from curling up again. For the even distribution of the 

 weight it is well to make a tripod with three specimens 

 and the cover-slip. 



Next day the creatures will be found to be rigid, and 

 ready for dry mounting. If they are to be made trans- 

 parent, carbolic acid is substituted for the formalin, 

 which is remo\ed by means of blotting paper as the 

 acid is added. Some species will require a very much 

 longer time in the carbolic acid than others, but they 

 simply remain in till clear, when they are ready for 

 mounting in Canada balsam, and the collector then has 

 one specimen which shows how the animal looks when 

 alive, and another in which minute points of the exter- 

 nal anatomy may be studied. In this particular group 

 of mites the chitinous cuticle is generally well-developed, 



